Medical robotic system having entry guide controller with instrument tip velocity limiting

ABSTRACT

A medical robotic system includes an entry guide with articulatable instruments extending out of its distal end, an entry guide manipulator providing controllable four degrees-of-freedom movement of the entry guide, and a controller configured to limit joint velocities in the entry guide manipulator so as to prevent movement of tips of the articulatable instruments from exceeding a maximum allowable linear velocity when the entry guide manipulator is being used to move the entry guide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/163,069,filed Jun. 27, 2008, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to medical robotic systems andin particular, to a medical robotic system having articulatableinstruments extending out of an entry guide and an entry guidecontroller for moving the entry guide without exceeding a maximumallowable linear velocity for tips of the articulatable instruments.

BACKGROUND OF THE INVENTION

Medical robotic systems such as teleoperative systems used in performingminimally invasive surgical procedures offer many benefits overtraditional open surgery techniques, including less pain, shorterhospital stays, quicker return to normal activities, minimal scarring,reduced recovery time, and less injury to tissue. Consequently, demandfor such medical robotic systems is strong and growing.

One example of such a medical robotic system is the da Vinci® SurgicalSystem from Intuitive Surgical, Inc., of Sunnyvale, Calif., which is aminimally invasive robotic surgical system. The da Vinci® SurgicalSystem has a number of robotic arms that move attached medical devices,such as an image capturing device and Intuitive Surgical's proprietaryEndoWrist® articulating surgical instruments, in response to movement ofinput devices by a surgeon viewing images captured by the imagecapturing device of a surgical site. Each of the medical devices isinserted through its own minimally invasive incision into the patientand positioned to perform a medical procedure at the surgical site. Theincisions are placed about the patient's body so that the surgicalinstruments may be used to cooperatively perform the medical procedureand the image capturing device may view it without their robotic armscolliding during the procedure.

To perform certain medical procedures, it may be advantageous to use asingle entry aperture, such as a minimally invasive incision or anatural body orifice, to enter a patient to perform a medical procedure.For example, an entry guide may first be inserted, positioned, and heldin place in the entry aperture. Instruments such as an articulatablecamera and a plurality of articulatable surgical tools, which are usedto perform the medical procedure, may then be inserted into a proximalend of the entry guide so as to extend out of its distal end. Thus, theentry guide provides a single entry aperture for multiple instrumentswhile keeping the instruments bundled together as it guides them towardthe work site.

To properly guide the instruments to and maneuver them about a work sitewithin a patient, an entry guide manipulator commandable throughoperator interaction with one or more input devices is desirable to movethe entry guide through and about a pivot point at the entry aperture.In doing so, however, it is important for the safety of the patient andthe instruments extending out of the distal end of the entry guide thatthe linear velocity of the instrument tips be controlled as the entryguide moves. Therefore, it is desirable to restrict the linear velocityof the instrument tips to a maximum allowable linear velocity.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, one object of one or more aspects of the present inventionis a method for positioning and orienting an entry guide that guides acamera and at least one surgical tool through a single entry aperture ina patient to a work site in the patient.

Another object of one or more aspects of the present invention is amethod for moving an entry guide without exceeding a maximum allowablelinear velocity of a tip of an articulatable instrument extending out ofa distal end of the entry guide.

Another object of one or more aspects of the present invention is amedical robotic system including a controller for moving an entry guidewithout exceeding a maximum allowable linear velocity on movement of atip of an articulatable instrument extending out of a distal end of theentry guide.

These and additional objects are accomplished by the various aspects ofthe present invention, wherein briefly stated, one aspect is a methodfor positioning and orienting an entry guide that guides a camera and atleast one surgical tool through a single entry aperture in a patient toa work site within the patient, the method comprising: receiving animage referenced command indicative of a desired state of an imagerelative to eyes of an operator, wherein the image is derived from dataprovided by the camera and displayed on a display screen so as to beviewable by the operator; processing the image referenced command togenerate a camera command so that a state of a tip of the cameraprovides the desired state of the image being displayed on the displayscreen; processing the camera command to generate an entry guide commandso that a state of a distal tip of the entry guide provides the desiredstate of the image being displayed on the display screen; and processingthe entry guide command to generate joint actuator commands so that anentry guide manipulator manipulates the entry guide so that the cameraprovides data from which the desired state of the image is derived.

Another aspect is a method for moving an entry guide without exceeding amaximum allowable linear velocity of a tip of an articulatableinstrument extending out of a distal end of the entry guide, the methodcomprising: determining desired states of mechanical elements foreffecting a desired state of the entry guide; determining a length thatthe tip of the articulatable instrument extends beyond the distal end ofthe entry guide; limiting the desired movements of the mechanicalelements so as to avoid exceeding the maximum allowable linear velocityon the tip of the articulatable instrument; and commanding themechanical elements to move in response to the limited desired movementsof the mechanical elements.

Another aspect is a medical robotic system comprising: an entry guide;an entry guide manipulator for manipulating the entry guide relative toa remote center; a plurality of articulatable instruments extendingthrough the entry guide and out of a distal end of the entry guide, theplurality of articulatable instruments including an articulatablecamera; an input device; and a controller configured to control movementof the entry guide through the entry guide manipulator in response tomovement of the input device without exceeding a maximum allowablelinear velocity of tips of the plurality of articulatable instruments.

Another aspect is a method for positioning and orienting an entry thatguides a camera to a work site, comprising: processing and displayingimages periodically captured by the camera on a display screen;disassociating a first input device from a first articulatable tool, anddisassociating a second input device from a second articulatable tool;associating the first and second input devices with the entry guide;generating an image referenced control from translational movement ofthe first and second input devices; positioning and orienting the entryguide in response to the image referenced command; maintainingorientational alignment between the first input device and the firstarticulatable tool by feeding back information of an orientation of thefirst articulatable tool back to the first input device so as to causeorientational movement of the first input device when the first inputdevice and the first articulatable tool are orientationally out ofalignment, and maintaining orientational alignment between the secondinput device and the second articulatable tool by feeding backinformation of an orientation of the second articulatable tool back tothe second input device so as to cause orientational movement of thesecond input device when the second input device and the secondarticulatable tool are orientationally out of alignment; disassociatingthe first and second input devices from the entry guide; andre-associating the first input device with the first articulatable tool,and re-associating the second input device with the second articulatabletool.

Additional objects, features and advantages of the various aspects ofthe present invention will become apparent from the followingdescription of its preferred embodiment, which description should betaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a top view of an operating room employing a medicalrobotic system utilizing aspects of the present invention.

FIG. 2 illustrates a block diagram of components for controlling andselectively associating device manipulators to left and righthand-manipulatable input devices in a medical robotic system utilizingaspects of the present invention.

FIG. 3 illustrates a perspective view of a distal end of an entry guidewith a plurality of articulatable instruments extending out of it, asused in a medical robotic system utilizing aspects of the presentinvention.

FIG. 4 illustrates a cross-sectional view of an entry guide as used in amedical robotic system utilizing aspects of the present invention.

FIG. 5 illustrates a perspective view of an entry guide along with fourdegrees-of-freedom movement as used in a medical robotic systemutilizing aspects of the present invention.

FIG. 6 illustrates a block diagram of interacting components of an entryguide manipulator as used in a medical robotic system utilizing aspectsof the present invention.

FIG. 7 illustrates a block diagram of an entry guide controller used tocontrol an entry guide manipulator in a medical robotic system utilizingaspects of the present invention.

FIG. 8 illustrates a flow diagram of a method for moving an entry guidewithout exceeding a maximum allowable linear velocity on movement of atip of an articulatable instrument extending out of a distal end of theentry guide, utilizing aspects of the present invention.

FIG. 9 illustrates a flow diagram of a method for limiting entry guidemanipulator joint velocities to avoid excessive instrument tipvelocities as used in a medical robotic system utilizing aspects of thepresent invention.

FIG. 10 illustrates a side view of an entry guide with various referenceframes and measurements indicated thereon as used in a medical roboticsystem utilizing aspects of the present invention.

FIG. 11 illustrates reference frames for left and right input devicesand a set-point defined between the input devices as used in a medicalrobotic system utilizing aspects of the present invention.

FIG. 12 illustrates a side view of an entry guide with various vectorsindicated thereon as used in a medical robotic system utilizing aspectsof the present invention.

FIG. 13 illustrates a perspective view of an entry guide with angularvelocity vectors defined thereon as used in a medical robotic systemutilizing aspects of the present invention.

FIG. 14 illustrates a block diagram of an entry guide manipulator in/out(I/O) joint velocity and position limiting as used in a medical roboticsystem utilizing aspects of the present invention.

FIG. 15 illustrates a block diagram of an entry guide manipulator yawjoint velocity and position limiting as used in a medical robotic systemutilizing aspects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates, as an example, a top view of an operating room inwhich a medical robotic system 100 is being utilized by a Surgeon 20 forperforming a medical procedure on a Patient 40 who is lying face up onan operating table 50. One or more Assistants 30 may be positioned nearthe Patient 40 to assist in the procedure while the Surgeon 20 performsthe procedure teleoperatively by manipulating input devices 108, 109 ona surgeon console 10.

In the present example, an entry guide (EG) 200 is inserted through asingle entry aperture 150 into the Patient 40. Although the entryaperture 150 is a minimally invasive incision in the present example, inthe performance of other medical procedures, it may instead be a naturalbody orifice. The entry guide 200 is held and manipulated by a roboticarm assembly 130.

As with other parts of the medical robotic system 100, the illustrationof the robotic arm assembly 130 is simplified in FIG. 1. In one exampleof the medical robotic system 100, the robotic arm assembly 130 includesa setup arm and an entry guide manipulator. The setup arm is used toposition the entry guide 200 at the entry aperture 150 so that itproperly enters the entry aperture 150. The entry guide manipulator isthen used to robotically insert and retract the entry guide 200 into andout of the entry aperture 150. It may also be used to robotically pivotthe entry guide 200 in pitch, roll and yaw about a pivot point locatedat the entry aperture 150. An example of such an entry guide manipulatoris the entry guide manipulator 202 of FIG. 2 and an example of the fourdegrees-of-freedom movement that it manipulates the entry guide 200 withis shown in FIG. 5.

The console 10 includes a 3-D monitor 104 for displaying a 3-D image ofa surgical site to the Surgeon, left and right hand-manipulatable inputdevices 108, 109, and a processor (also referred to herein as a“controller”) 102. The input devices 108, 109 may include any one ormore of a variety of input devices such as joysticks, gloves,trigger-guns, hand-operated controllers, or the like. Other inputdevices that are provided to allow the Surgeon to interact with themedical robotic system 100 include a foot pedal 105, a conventionalvoice recognition system 160 and a Graphical User Interface (GUI) 170.

The console 10 is usually located in the same room as the Patient sothat the Surgeon may directly monitor the procedure, is physicallyavailable if necessary, and is able to speak to the Assistant(s)directly rather than over the telephone or other communication medium.However, it will be understood that the Surgeon can also be located in adifferent room, a completely different building, or other remotelocation from the Patient allowing for remote surgical procedures.

As shown in FIG. 3, the entry guide 200 has articulatable instrumentssuch as articulatable surgical tools 231, 241 and an articulatablestereo camera 211 extending out of its distal end. The camera has a pairof stereo image capturing devices 311, 312 and a fiber optic cable 313(coupled at its proximal end to a light source) housed in its tip. Thesurgical tools 231, 241 have end effectors 331, 341. Although only twotools 231, 241 are shown, the entry guide 200 may guide additional toolsas required for performing a medical procedure at a work site in thePatient. For example, as shown in FIG. 4, a passage 351 is available forextending another articulatable surgical tool through the entry guide200 and out through its distal end. Each of the surgical tools 231, 241is associated with one of the input devices 108, 109 in a tool followingmode. The Surgeon performs a medical procedure by manipulating the inputdevices 108, 109 so that the controller 102 causes correspondingmovement of their respectively associated surgical tools 231, 241 whilethe Surgeon views the work site in 3-D on the console monitor 104 asimages of the work site are being captured by the articulatable camera211.

Preferably, input devices 108, 109 will be provided with at least thesame degrees of freedom as their associated tools 231, 241 to providethe Surgeon with telepresence, or the perception that the input devices108, 109 are integral with the tools 231, 241 so that the Surgeon has astrong sense of directly controlling the tools 231, 241. To this end,the monitor 104 is also positioned near the Surgeon's hands so that itwill display a projected image that is oriented so that the Surgeonfeels that he or she is actually looking directly down onto the worksite and images of the tools 231, 241 appear to be located substantiallywhere the Surgeon's hands are located.

In addition, the real-time image on the monitor 104 is preferablyprojected into a perspective image such that the Surgeon can manipulatethe end effectors 331, 341 of the tools 231, 241 through theircorresponding input devices 108, 109 as if viewing the work site insubstantially true presence. By true presence, it is meant that thepresentation of an image is a true perspective image simulating theviewpoint of an operator that is physically manipulating the endeffectors 331, 341. Thus, the processor 102 transforms the coordinatesof the end effectors 331, 341 to a perceived position so that theperspective image being shown on the monitor 104 is the image that theSurgeon would see if the Surgeon was located directly behind the endeffectors 331, 341.

The processor 102 performs various functions in the system 100. Oneimportant function that it performs is to translate and transfer themechanical motion of input devices 108, 109 through control signals overbus 110 so that the Surgeon can effectively manipulate devices, such asthe tools 231, 241, camera 211, and entry guide 200, that areselectively associated with the input devices 108, 109 at the time.Another function is to perform various methods and implement variouscontrollers described herein.

Although described as a processor, it is to be appreciated that theprocessor 102 may be implemented in practice by any combination ofhardware, software and firmware. Also, its functions as described hereinmay be performed by one unit or divided up among different components,each of which may be implemented in turn by any combination of hardware,software and firmware. Further, although being shown as part of or beingphysically adjacent to the console 10, the processor 102 may alsocomprise a number of subunits distributed throughout the system.

For additional details on the construction and operation of variousaspects of a medical robotic system such as described herein, see, e.g.,U.S. Pat. No. 6,493,608 “Aspects of a Control System of a MinimallyInvasive Surgical Apparatus,” and U.S. Pat. No. 6,671,581 “CameraReferenced Control in a Minimally Invasive Surgical Apparatus,” whichare incorporated herein by reference.

FIG. 2 illustrates, as an example, a block diagram of components forcontrolling and selectively associating device manipulators to the inputdevices 108, 109. Various surgical tools such as graspers, cutters, andneedles may be used to perform a medical procedure at a work site withinthe Patient. In this example, two surgical tools 231, 241 are used torobotically perform the procedure and the camera 211 is used to view theprocedure. The instruments 231, 241, 211 are inserted through passagesin the entry guide 200. As described in reference to FIG. 1, the entryguide 200 is inserted into the Patient through entry aperture 150 usingthe setup portion of the robotic arm assembly 130 and maneuvered by theentry guide manipulator (EGM) 202 of the robotic arm assembly 130towards the work site where the medical procedure is to be performed.

Each of the devices 231, 241, 211, 200 is manipulated by its ownmanipulator. In particular, the camera 211 is manipulated by a cameramanipulator (ECM) 212, the first surgical tool 231 is manipulated by afirst tool manipulator (PSM1) 232, the second surgical tool 241 ismanipulated by a second tool manipulator (PSM2) 242, and the entry guide200 is manipulated by an entry guide manipulator (EGM) 202. So as to notoverly encumber the figure, the devices 231, 241, 211, 200 are notshown, only their respective manipulators 232, 242, 212, 202 are shownin the figure.

Each of the instrument manipulators 232, 242, 212 is a mechanicalassembly that carries actuators and provides a mechanical, sterileinterface to transmit motion to its respective articulatable instrument.Each instrument 231, 241, 211 is a mechanical assembly that receives themotion from its manipulator and, by means of a cable transmission,propagates it to the distal articulations (e.g., joints). Such jointsmay be prismatic (e.g., linear motion) or rotational (e.g., they pivotabout a mechanical axis). Furthermore, the instrument may have internalmechanical constraints (e.g., cables, gearing, cams and belts, etc.)that force multiple joints to move together in a pre-determined fashion.Each set of mechanically constrained joints implements a specific axisof motion, and constraints may be devised to pair rotational joints(e.g., joggle joints). Note also that in this way the instrument mayhave more joints than the available actuators.

In contrast, the entry guide manipulator 202 has a differentconstruction and operation. A description of the parts and operation ofthe entry guide manipulator 202 is described below in reference to FIG.6.

In this example, each of the input devices 108, 109 may be selectivelyassociated with one of the devices 211, 231, 241, 200 so that theassociated device may be controlled by the input device through itscontroller and manipulator. For example, by placing switches 258, 259 intheir respective tool following modes “T2” and “T1”, the left and rightinput devices 108, 109 may be respectively associated with the first andsecond surgical tools 231, 241, which are telerobotically controlledthrough their respective controllers 233, 243 (preferably implemented inthe processor 102) and manipulators 232, 242 so that the Surgeon mayperform a medical procedure on the Patient while the entry guide 200 islocked in place.

When the camera 211 or the entry guide 200 is to be repositioned by theSurgeon, either one or both of the left and right input devices 108, 109may be associated with the camera 211 or entry guide 200 so that theSurgeon may move the camera 211 or entry guide 200 through itsrespective controller (213 or 203) and manipulator (212 or 202). In thiscase, the disassociated one(s) of the surgical tools 231, 241 is lockedin place relative to the entry guide 200 by its controller. For example,by placing switches 258, 259 respectively in camera positioning modes“C2” and “C1”, the left and right input devices 108, 109 may beassociated with the camera 211, which is telerobotically controlledthrough its controller 213 (preferably implemented in the processor 102)and manipulator 212 so that the Surgeon may position the camera 211while the surgical tools 231, 241 and entry guide 200 are locked inplace by their respective controllers 233, 243, 203. If only one inputdevice is to be used for positioning the camera, then only one of theswitches 258, 259 is placed in its camera positioning mode while theother one of the switches 258, 259 remains in its tool following mode sothat its respective input device may continue to control its associatedsurgical tool.

On the other hand, by placing switches 258, 259 respectively in entryguide positioning modes “G2” and “G1”, the left and right input devices108, 109 may be associated with the entry guide 200, which istelerobotically controlled through its controller 203 (preferablyimplemented in the processor 102) and manipulator 202 so that theSurgeon may position the entry guide 200 while the surgical tools 231,241 and camera 211 are locked in place relative to the entry guide 200by their respective controllers 233, 243, 213. As with the camerapositioning mode, if only one input device is to be used for positioningthe entry guide, then only one of the switches 258, 259 is placed in itsentry guide positioning mode while the other one of the switches 258,259 remains in its current mode.

The selective association of the input devices 108, 109 to other devicesin this example may be performed by the Surgeon using the GUI 170 or thevoice recognition system 160 in a conventional manner. Alternatively,the association of the input devices 108, 109 may be changed by theSurgeon depressing a button on one of the input devices 108, 109 ordepressing the foot pedal 105, or using any other well known modeswitching technique.

As shown in a perspective view of the entry guide 200 in FIG. 5, theentry guide 200 is generally cylindrical in shape and has a longitudinalaxis X′ running centrally along its length. The pivot point, which isalso referred to as a remote center “RC”, serves as an origin for both afixed reference frame having X, Y and Z axes as shown and an entry guidereference frame having X′, Y′ and Z′ axes as shown. When the system 100is in the entry guide positioning mode, the entry guide manipulator 202is capable of pivoting the entry guide 200 in response to movement ofone or more associated input devices about the Z axis (which remainsfixed in space) at the remote center “RC” in yaw ψ. In addition, theentry guide manipulator 202 is capable of pivoting the entry guide 200in response to movement of the one or more input devices about the Y′axis (which is orthogonal to the longitudinal axis X′ of the entry guide200) in pitch θ, capable of rotating the entry guide 200 about itslongitudinal axis X′ in roll Φ, and linearly moving the entry guide 200along its longitudinal axis X′ in insertion/retraction or in/out “I/O”directions in response to movement of the one or more associated inputdevices. Note that unlike the Z-axis which is fixed in space, the X′ andY′ axes move with the entry guide 200.

As shown in FIG. 6, the entry guide manipulator (EGM) 202 has fouractuators 601-604 for actuating the four degrees-of-freedom movement ofthe entry guide 200 (i.e., yaw ψ, pitch θ, roll Φ, and in/out I/O) andfour corresponding assemblies 611-614 to implement them.

The EGM yaw assembly 611 includes a yaw rotary joint which is a part ofthe robotic arm assembly 130 that maintains its coordinate position inthree-dimensional space while the entry guide manipulator 202 moves theentry guide 200. The EGM yaw assembly 611 further includes one or morelinks that couple it through other parts of the entry guide manipulator202 to the entry guide 200 so that when the EGM yaw actuator 601 (e.g.,a motor) actuates (e.g., rotates) the yaw rotary joint, the entry guide200 is rotated about the fixed Z-axis at the remote center RC in yaw ψ.

The EGM pitch assembly 612 includes a pitch rotary joint which is a partof the robotic arm assembly that moves with the entry guide 200. The EGMpitch assembly 612 further includes one or more links that couple itthrough other parts of the entry guide manipulator 202 to the entryguide 200 so that when the EGM pitch actuator 602 (e.g., a motor)actuates (e.g., rotates) the pitch rotary joint, the entry guide 200 isrotated about the Y′-axis at the remote center RC in pitch θ.

The EGM roll assembly 613 includes a gear assembly that couples theentry guide 200 to the EGM roll actuator 603 so that when the EGM rollactuator 603 (e.g., a motor) actuates (e.g., its rotor rotates), theentry guide 200 also rotates about its longitudinal axis X′ in response.

The EGM I/O assembly 614, on the other hand, includes a prismatic jointthat is coupled to the EGM I/O actuator 604 so that when the EGM I/Oactuator 604 (e.g., a motor) actuates (e.g., its rotor rotates), therotary action is transferred into a linear displacement of the entryguide 200 along its longitudinal axis X′.

FIG. 7 illustrates, as an example, a block diagram of a controller 700(which is one version of the controller 203) for controlling movement ofthe entry guide 200 in response to movement of the input devices 108,109 when the input devices 108, 109 are selectively associated with theentry guide 200 in their respective entry guide positioning modes “G2”and “G1”. In this example, both input devices 108, 109 are used to movethe entry guide 200 as the Surgeon views images captured by the camera211. The articulatable camera 211, which extends out of the distal endof the entry guide 200, is “soft” locked (through its controller 213) atits current position relative to the entry guide 200 during the entryguide positioning mode.

Thus, an image referenced control is implemented in the controller 700so that the controller 700 controls movement of the entry guide 200while the Surgeon is given the impression that he or she is moving theimage captured by the camera 211. In particular, the Surgeon is providedwith the sensation that he or she is grasping the image being displayedon the monitor 104 with his or her left and right hands and moving theimage about the work site to a desired viewing point. Note that underthis type of control, the image on the monitor 104 appears to move inopposite directions in response to movement of the input devices 108,109. For example, the image moves to the right when the input devices108, 109 are moved to the left (and vice versa) and the image moves upwhen the input devices 108, 109 are moved down (and vice versa).

The input devices 108, 109 include a number of links connected by jointsso as to facilitate multiple degrees-of-freedom movement. For example,as the Surgeon moves the input devices 108, 109 from one position toanother, sensors associated with the joints of the input devices 108,109 sense such movement at sampling intervals (appropriate for theprocessing speed of the controller 102 and entry guide control purposes)and provide digital information indicating such sampled movement injoint space to input processing blocks 710, 720.

As shown in FIG. 11, each of the input devices 108, 109 has a pivotpoint (also referred to herein as a “control point”) and a referenceframe centered at the pivot point. The input devices 108, 109 providethree translational degrees-of-freedom movement (e.g., forward/backalong their respective longitudinal axes X_(LM), X_(RM) of theirgrippers 1101, 1111; side-to-side along first axes Y_(LM), Y_(RM)orthogonal to the longitudinal axes X_(LM), X_(RM); and up/down alongsecond axes Z_(LM), Z_(RM) orthogonal to the first axes Y_(LM), Y_(RM)and longitudinal axes X_(LM), X_(RM)) for their respective pivot points1102, 1112 of their grippers 1101, 1111. The input devices 108, 109 alsoprovide three orientational degrees-of-freedom movement (e.g., rollabout their respective longitudinal axes X_(LM), X_(RM); pitch abouttheir respective first axes Y_(LM), Y_(RM); and yaw about theirrespective second axes Z, Z_(RM)) for their respective pivot points1102, 1112 of their grippers 1101, 1111. In addition, squeezing theirrespective grippers 1101, 1111 may provide additional degrees-of-freedomfor manipulating end effectors of surgical tools respectively associatedwith the input devices 108, 109 at the time.

Input processing blocks 710, 720 process the information received fromthe joint sensors of the input devices 108, 109 to transform theinformation into corresponding desired positions and velocities for theimage being displayed on the monitor 104 in a Cartesian space relativeto a reference frame associated with the Surgeon's eyes (the “eyereference frame”) by computing, for example, joint velocities from thejoint position information or, alternatively, using velocity sensors)and performing the transformation using a Jacobian matrix and eyerelated information using well-known transformation techniques.

Scale and offset processing blocks 701, 702 receive the processedinformation 711, 713 from the input processing blocks 710, 720, convertthe desired positions and velocities to camera tip positions andvelocities in the reference frame of the entry guide 200, and applyscale and offset adjustments to the information so that the resultingmovement of the camera 211 and consequently, the image being viewed onthe monitor 104 appears natural and as expected by the operator of theinput devices 108, 109. The scale adjustment is useful where smallmovements of the camera 211 are desired relative to larger movement ofthe input devices 108, 109 in order to allow more precise movement ofthe camera 211 as it views the work site. To implement the sharedcontrol for moving the camera 211 by the input devices 108, 109, lateraloffsets are applied to shift the control point to the left for the inputdevice 108 which is being operated by the left hand of the operator andto the right for the input device 109 which is being operated by theright hand of the operator so that each of the input devices 108, 109appears to control a corresponding view of the stereoscopic image beingdisplayed on the monitor 104. In addition, offset adjustments areapplied for aligning the input devices 108, 109 with respect to theSurgeon's eyes as he or she manipulates the input devices 108, 109 tocommand movement of the camera 211 and consequently, its captured imagethat is being displayed at the time on the monitor 104.

The outputs 721, 722 of the scale and offset blocks 701, 702 areprovided to a set-point generation block 703 so that a single set ofposition and velocity commands for the camera tip 311 in the referenceframe of the entry guide 200 is provided for the entry guide manipulator202. Therefore, as the operator moves the input devices 108, 109, he orshe forces a motion on the mid-point of what feels like to the operatorto be a “virtual handlebar”. This motion is then “transferred” tosubsequent blocks of the controller 700 as a set-point for Cartesianmotions.

Up to this point, the controller 700 has treated the operator movementof the input devices 108, 109 as commanding a corresponding movement ofthe camera 211 using image referenced control. Ultimately, however, itis the entry guide manipulator 202, not the camera manipulator 213 thatis to be moved in response to the operator commands. Therefore, aninverse “entry guide-to-camera” transform (^(EG)X_(CAM))⁻¹ block 751converts the desired movement of the tip of the camera 211 into adesired movement of the tip of the entry guide 202 while still in thereference frame of the entry guide.

A simulated entry guide manipulator block 704 receives the output 724 ofthe inverse “entry guide-to-camera” transform (^(EG)X_(CAM))⁻¹ block 751and transforms the commanded position and velocity for the distal end ofthe entry guide 200 from its Cartesian space to corresponding desiredjoint positions and velocities for the entry guide manipulator (EGM) 202(e.g., EGM joint space) using the known inverse kinematics of the entryguide manipulator 202 and characteristics of the entry guide 200. Indoing so, the simulated entry guide manipulator block 704 avoidssingularities and limits the commanded joint positions and velocities toavoid physical limitations. In addition, it implements a method formoving the entry guide 200 without exceeding a velocity limit of a tipof an articulatable surgical instrument extending out of a distal end ofthe entry guide 200 as described in reference to FIG. 8.

The output 725 of the simulated entry guide manipulator block 704 isthen provided to an EGM joint controller block 705 and a forwardkinematics block 706. The joint controller block 705 includes a jointcontrol system for each controlled joint (i.e., each mechanical elementcontrolling one of the four degrees-of-freedom described in reference toFIG. 5) of the entry guide manipulator 202, and the output 725 of thesimulated entry guide manipulator block 704 provides, as its inputs, thecommanded value for each joint of the entry guide manipulator 202. Forfeedback control purposes, sensors associated with each of thecontrolled joints of the entry guide manipulator 202 provide sensor data732 back to the joint controller block 705 indicating the currentposition and/or velocity of each joint of the entry guide manipulator202. The sensors may sense this joint information either directly (e.g.,from the joint on the entry guide manipulator 202) or indirectly (e.g.,from the actuator in the entry guide manipulator 202 driving the joint).Each joint control system in the joint controller 705 then generatestorque or other appropriate commands for its respective actuator (e.g.,motor) in the entry guide manipulator 202 so as to drive the differencebetween the commanded and sensed joint values to zero in a conventionalfeedback control system manner.

The forward kinematics block 706 transforms the output 725 of thesimulated entry guide manipulator block 704 from joint space back to theCartesian space of the entry guide manipulator 202 using the forwardkinematics of the entry guide manipulator 202. The output of the forwardkinematics block 706 is then translated in an “entry guide-to-camera”transformation (^(EG)X_(CAM)) block 752 so that the controller 700operates once again in camera referenced control mode.

The scale and offset blocks 701, 702 perform an inverse scale and offsetfunctions on the output 742 of the “entry guide-to-camera”transformation (^(EG)X_(CAM)) block 752 (as well as performing areversal of the set-point generation) before passing their respectiveoutputs 712, 714 to the input processing blocks 710, 720 where errorvalues are calculated between their respective outputs 711, 713 andinputs 712, 714. If no limitation or other constraint had been imposedon the input 724 to the simulated entry guide manipulator block 704,then the calculated error values would be zero. On the other hand, if alimitation or constraint had been imposed, then the error value is notzero and it is converted to a torque command that drives actuators inthe input devices 108, 109 to provide force feedback felt by the handsof their operator. Thus, the operator becomes aware that a limitation orconstraint is being imposed by the force that he or she feels resistinghis movement of the input devices 108, 109 in that direction. Inaddition to this force feedback, forces coming from other sensors oralgorithms may be superimposed on the force feedback.

An output 741 of the forward kinematics block 706 may also be providedto the simulated entry guide manipulator block 704 for control purposes.For example, the simulated position output may be fed back and comparedwith the commanded position.

FIG. 8 illustrates, as an example, a flow diagram of a method, which maybe implemented in the controller 700, for moving the entry guide 200without exceeding a maximum allowable linear velocity on movement of atip of an articulatable instrument (e.g., 211, 231 and 241 in FIG. 3)extending out of a distal end (e.g., tip) of the entry guide 200. Notethat unlike a position limit which would prevent reaching positionsbeyond the limit, a velocity limit does not restrict the set ofreachable positions but forces the Surgeon to perform potentiallydangerous motions in a slower way.

In applying the method, a number of reference frames is used. On theinput side, the Surgeon views an image captured by the camera 211 on theconsole monitor 104 while the Surgeon controls the input devices 108,109 to move the effectively image and consequently, in the entry guidepositioning mode “G”, the entry guide 200 (using image referencedcontrol). Thus, an eye reference frame <EYE> is used on the input sidethat is based upon the position of the Surgeon's eyes as the Surgeonviews the monitor 104 and manipulates the input devices 108, 109. On theentry guide side, as shown in FIG. 10, a camera reference frame <CAM>represents what the Surgeon is seeing at the time on the monitor 104, anentry guide tip reference frame <EG> represents what the controller 700controls in entry guide positioning mode “G”, an articulatableinstrument tip reference frame <TIP> represents what needs to bevelocity limited, and a remote center reference frame <REF> represents afixed reference frame.

In 801, the method first determines transforms that relate the tip(i.e., distal end) of the entry guide 200 to the tips of each of theinstruments 211, 231, 241 that are extending out of the distal end ofthe entry guide 200. Mathematically such transforms may be representedas follows for the present example: ^(EG)X₁ for the first surgical tool231, ^(EG)X₂ for the second surgical tool 241, and ^(EG)X_(CAM) for thecamera 211.

The method then decomposes the positions of the instruments 211, 231,241 into radial and tangential components with respect to the tip of theentry guide 200. For example, as shown in FIG. 12, a position 1220 of atip 1202 of an instrument to the distal end 1201 of the entry guide 200is shown decomposed into a radial component 1221 and tangentialcomponent 1222. Mathematically, this may be represented as follows forthe three instruments:^(EG) {right arrow over (P)} ₁=^(EG) {right arrow over (P)}_(1,RAD)+^(EG) {right arrow over (P)} _(1,TAN)^(EG) {right arrow over (P)} ₂=^(EG) {right arrow over (P)}_(2,RAD)+^(EG) {right arrow over (P)} _(2,TAN)^(EG) {right arrow over (P)} _(CAM)=^(EG) {right arrow over (P)}_(CAM,RAD)+^(EG) {right arrow over (P)} _(CAM,TAN)

Weight coefficients “α”, based upon some criteria, may be assigned toeach of the instruments to increase its effect in limiting the entryguide manipulator (EGM) 202 joint velocities. One criterion, forexample, may be that instruments having end effectors or tips fallingoutside of the field of view of the camera 211 can have a larger weightcoefficient and thus a larger impact on controlling EGM jointvelocities. Another criterion, may be the distance that the instrumentsare from a specified part of the patient's anatomy (e.g., if CRT scansare available that may be registered to the patient, a certain area canbe marked as delicate and thus the weighting coefficients of theinstruments can be increased as they approach it). Mathematically, thismay be represented as follows for three instruments:^(EG) {right arrow over (P)} _(W1)=α₁ ^(EG) {right arrow over (P)} ₁^(EG) {right arrow over (P)} _(W2)=α₂ ^(EG) {right arrow over (P)} ₂^(EG) {right arrow over (P)} _(WCAM)=α_(CAM) ^(EG) {right arrow over(P)} _(WCAM,RAD)+^(EG) {right arrow over (P)} _(WCAM,TAN)

Note that the weighting factor for the camera is computed according to aslightly different criterion than the other instruments. In particular,the camera's weighting factor accounts for the camera tip's extensionalong the I/O direction and its elevation above that axis (i.e., howmuch it is “joggled up”). This is because the distal articulations ofthe camera instrument 211 (which are invisible to the user) might touchtissues as the camera tip 311 is moved.

In 802, the method receives a desired camera tip Cartesian position andvelocity, such as the output 723 which is received by the inverse “entryguide-to-camera” transform (^(EG)X_(CAM))⁻¹ block 751 from the set-pointgeneration block 703 of the controller 700.

In 803, the method converts the received desired camera tip Cartesianposition and velocity to a corresponding desired entry guide tip (i.e.,distal end) position and velocity, such as performed by the inverse“entry guide-to-camera” transform (^(EG)X_(CAM))⁻¹ block 751 to generateits output 724. The method then translates the desired entry guide tipposition and velocity to the remote center reference frame using knowngeometries of the entry guide 200, such as may be performed in thesimulated entry guide manipulator block 704 of the controller 700.

In 804, the method determines desired joint velocities for the entryguide manipulator 202 from the desired entry guide tip position andvelocity in the remote center reference frame using known kinematics ofthe entry guide manipulator 202, such as may be performed in thesimulated entry guide manipulator block 704 of the controller 700. Inexample, four joint velocities for the entry guide manipulator 202 aredetermined, one for each of the four degrees of freedom, i.e., desiredyaw, pitch, I/O and roll joint velocities (where the term “joint” isunderstood herein to mean a mechanical element used to effectuate thedegree-of-freedom).

In 805, the method limits the desired EGM joint velocities to avoidexcessive instrument tip velocities. One technique for doing so isdescribed in reference to FIG. 9 herein. In addition, the method alsoensures that physical limitations on the EGM joints are not exceededbefore generating position and velocity commands to drive the joints ofthe entry guide manipulator 202, such as done in the simulated entryguide manipulator block 704 of FIG. 7.

After completing 805, the method then loops back to 802 to process anext sampled movement of the input devices 108, 109 through 802-805. Inthis case, the positions and orientations of the instruments 211, 231,241 are presumed to be “soft-locked” in place by their respectivecontrollers during the entry guide positioning mode “G”. Therefore, thetransforms and positions determined in 801 relative to the entry guide200 remain constant and need not be re-determined.

FIG. 9 illustrates, as an example, a flow diagram of a method, which isimplemented in the simulated entry guide manipulator 704 of FIG. 7, forlimiting entry guide manipulator joint velocities to avoid excessiveinstrument tip velocities. As previously mentioned, the method isparticularly useful for performing 805 of FIG. 8.

In the present example, four EGM joint velocities are to be limited—theyaw, pitch, roll and I/O as shown and described in reference to FIG. 5.Of these joint velocities, only the I/O results in the same velocity forthe entry guide tip and the instrument tip. In pitch and yaw, theinstrument tip velocities are larger than the entry guide tip velocitybecause of the larger radius of rotation about the remote center (see,e.g., r₁ vs. r_(EG) in FIG. 10). In roll, the tangential component ofthe instrument tip position needs to be taken into account as acontributor to the instrument tip velocity (see, e.g., tangentialcomponent 1222 in FIG. 12).

Thus, in 901, the method first limits the desired movement of the EGMI/O joint to take advantage of the configuration of the entry guide 200and the instruments 211, 231, 241 extending out of the distal end of theentry guide 200 as noted above. One technique for limiting the movementof the EGM I/O joint is described with the visual aid of FIG. 14. First,the desired EGM I/O joint velocity {dot over (q)}_(IO,DES) is limited bya velocity limiter 1401 so that its output {dot over (q)}_(IO) is lessthan or equal to the velocity limit of the instrument tips. Anintegrator 1402 integrates the output {dot over (q)}_(IO) to generate adesired EGM I/O joint position q_(IO,DES) which is limited by a positionlimiter 1403 so that its output q_(IO) is less than or equal to amaximum allowable displacement of the EGM I/O joint.

In 902, the method determines the distance r_(EG) of the entry guide tipfrom the remote center in a straightforward manner using the EGM I/Ojoint position q_(IO), and in 903, the method determines the distances|^(RC){right arrow over (P)}_(W1)|, |^(RC){right arrow over (P)}_(W2)|of the instruments from the remote center in a straightforward mannerusing the positions ^(EG){right arrow over (P)}_(W1), ^(EG){right arrowover (P)}_(W2) of the instruments relative to the entry guide tip (aspreviously determined in 801 of FIG. 8) and the distance r_(EG) of theentry guide tip from the remote center (as determined in 902).

In 904, the method determines a resulting velocity {right arrow over(V)}_(1,DES), {right arrow over (V)}_(2,DES), {right arrow over(V)}_(CAM,DES) for each of the instruments 231, 241, 211 using thedesired EGM rotary joint velocities (as determined in 804 of FIG. 8) andthe instrument tip position from the remote center (as determined in903), such as in the following equation for the i^(th) instrument:

${\overset{\rightarrow}{V}}_{i,{DES}} = {{{J\left( {q_{EG},r_{i,{RAD}}} \right)}\begin{bmatrix}{\overset{.}{q}}_{{OY},{DES}} \\{\overset{.}{q}}_{{OP},{DES}} \\{\overset{.}{q}}_{{RO},{DES}}\end{bmatrix}} + {{\hat{X}}_{EG}^{\prime}{\overset{.}{q}}_{{RO},{DES}} \times {\overset{\rightarrow}{r}}_{i,{{TA}\; N}}}}$

where the term“J(q_(EG), r_(i,RAD))” is the EGM Jacobian computed byreplacing q_(IO) (as determined in 901) with a value that would placethe entry guide tip at a distance equal to the radial component of theinstrument tip position from the remote center, the term “

′_(EG)” is the current direction of the entry guide 200 along the I/Oaxis (i.e., the longitudinal axis X′ of the entry guide 200), “×” is thecross product, and the term “

′_(EG) {dot over (q)}_(RO,DES)×{right arrow over (r)}_(i,TAN)” accountsfor the additional contribution to velocity due to the fact that theentry guide 200 is rolling about the X′ axis.

A visual illustration of the resulting vector equation above is shown inFIG. 13 where vector 1311 represents the effect of roll about a circle1310 having radius equal to the tangential component of the positionvector for the instrument 1300, the vector 1312 represents the effect ofpitch and yaw about a sphere 1320 having radius equal to the radialcomponent of position vector relative to the remote center for theinstrument 1300, and axis 1301 is the EG I/O axis which coincides withthe longitudinal axis X′ of the entry guide 200.

In 905, the method determines a scale factor to be used for limiting theEGM joint rotary velocities. To do this, it first determines scalefactors for each of the instruments 231, 241, 211 using their respectiveresulting instrument tip velocities according to the followingequations:

$\sigma_{1} = \frac{V_{{MA}\; X}}{{\overset{\rightarrow}{V}}_{1,{DES}}}$$\sigma_{2} = \frac{V_{M\;{AX}}}{{\overset{\rightarrow}{V}}_{2,{DES}}}$$\sigma_{CAM} = \frac{V_{M\;{AX}}}{{\overset{\rightarrow}{V}}_{{CAM},{DES}}}$

where V_(MAX) is the maximum allowable velocity at the instrument tip.

The scale factor “σ” is then chosen to be the minimum scale factor ofall the scale factors calculated for the instruments 231, 241, 211extending out of the distal end of the entry guide 200.σ=min {σ₁,σ₂,σ_(CAM)}

In 906, the method applies the scale factor to generate saturated EGMrotary joint velocities. For example, for the EGM yaw joint velocity:

${\overset{.}{q}}_{{OY},{SAT}} = \left\{ \begin{matrix}{\overset{.}{q}}_{{OY},{DES}} & {{{if}\mspace{14mu}\sigma} \geq 1} \\{\sigma\;{\overset{.}{q}}_{{OY},{DES}}} & {{{if}\mspace{14mu}\sigma} < 1}\end{matrix} \right.$

The saturated EGM pitch and roll joint velocities may be similarlydetermined.

In 907, the saturated EGM rotary joint velocities are then subjected toconventional physical joint position and velocity limits to generatejoint commands for actuators which actuate the EGM rotary joints. Forexample, FIG. 15 illustrates a block diagram for limiting the EGM yawjoint position and velocity in which the saturated EGM yaw jointvelocity {dot over (q)}_(OY,SAT) is limited by a velocity limiter 1501so that its output {dot over (q)}_(OY) is less than or equal to thevelocity limit for the joint. An integrator 1502 integrates the output{dot over (q)}_(OY) to generate a desired EGM yaw joint positionq_(OY,DES) which is limited by a position limiter 1503 so that itsoutput q_(OY) is less than or equal to a maximum allowable displacementof the EGM yaw joint. The resulting desired EGM yaw joint velocity {dotover (q)}_(OY) and position q_(OY) are then provided, for example, asoutput of the simulated entry guide manipulator block 704 along with asimilarly determined EGM pitch velocity and position, similarlydetermined EGM roll velocity and position, and the previouslydetermined, in 901, EGM I/O velocity and position.

After positioning the entry guide 200, the input devices 108, 109 may bere-associated with their respective surgical tools 231, 241 (asdescribed in reference to FIG. 2). Before such re-association, however,it may be necessary to re-align the orientations of the input devices108, 109 with their surgical tools 231, 241 to provide a sense oftelepresence to the Surgeon. To avoid manual re-alignment by theSurgeon, using a conventional clutch mode for example, the operation ofthe input devices 108, 109 as a “virtual handlebar” may be takenadvantage of to automatically maintain the orientational alignmentbetween the input devices 108, 109 and the surgical tools 231, 241throughout the entry guide positioning process and therefore, eliminatethe need for manual re-alignment prior to such re-association.

One method for automatically maintaining orientational alignment betweenthe input devices 108, 109 and their respective surgical tools 231, 241is to feedback the surgical tools' sensed orientations to feedbackactuators of the input devices 108, 109 to control their orientationaldegrees-of-freedom (i.e., pitch, roll and yaw rotations about theirrespective control points 1102, 1112), even while the input devices 108,109 are associated with the entry guide 200. The remaining translationaldegrees-of-freedom of the input devices 108, 109 may then be used by theSurgeon to telerobotically position the entry guide 200 in its fourdegrees-of-freedom through the entry guide manipulator 202.

As an example, input devices 108, 109 may be moved up together in theirrespective Z_(LM), Z_(RM) axes to pitch the entry guide 200 downward ormoved down together to pitch the entry guide 200 upward. Also, the inputdevices 108, 109 may be moved to the right together in their respectiveY_(LM), Y_(RM) axes to yaw the entry guide to the left or moved to theleft to yaw the entry guide 200 to the right. The input devices 108, 109may be moved forward together in their respective X_(LM), X_(RM) axes tomove the entry guide 200 forward (in) and moved backward (out) togetherto move the entry guide 200 backward. Finally, the input devices 108,109 may be moved in opposite directions in their respective Z_(LM),Z_(RM) axes to roll the entry guide 200 about its longitudinal axis(e.g., moving input device 108 up and input device 109 down to roll theentry guide 200 to the right).

Although the various aspects of the present invention have beendescribed with respect to a preferred embodiment, it will be understoodthat the invention is entitled to full protection within the full scopeof the appended claims.

What is claimed is:
 1. A medical robotic system comprising: an entryguide; an entry guide manipulator for manipulating the entry guiderelative to a remote center; a plurality of articulatable instrumentsextending through the entry guide and out of a distal end of the entryguide, the plurality of articulatable instruments including a firstarticulatable instrument and an articulatable camera; an input device;and a controller configured to receive a desired state of thearticulatable camera from the input device, configured to determine adesired state of the entry guide to achieve the desired state of thearticulatable camera, configured to determine desired states ofmechanical elements of the entry guide manipulator for effecting thedesired state of the entry guide, and configured to command themechanical elements of the entry guide manipulator to be moved so as toeffect the desired state of the entry guide while limiting the movementsof the mechanical elements so as to avoid a resulting linear velocity ofa tip of the first articulatable instrument from exceeding a maximumallowable linear velocity for the tip of the first articulatableinstrument, wherein the linear velocity of the tip of the firstarticulatable instrument is determined using a length of the tip of thefirst articulatable instrument that extends beyond the distal end of theentry guide.
 2. The medical robotic system according to claim 1, whereinmovement of the input device indicates the desired state of thearticulatable camera relative to an image captured by the articulatablecamera, and wherein the controller is configured to determine thedesired states of the mechanical elements by determining the desiredstate of the entry guide to achieve the desired state of thearticulatable camera and is configured to determine the desired statesof the mechanical elements to achieve the desired state of the entryguide.
 3. The medical robotic system according to claim 2, wherein theentry guide is manipulatable by the entry guide manipulator so as tomove rotatably about a vertical axis passing through the remote center,linearly along a longitudinal axis of the entry guide passing throughthe remote center, rotatably about the longitudinal axis, and rotatablyabout a latitudinal axis orthogonal to longitudinal axis and passingthrough the remote center.
 4. The medical robotic system according toclaim 3, wherein the vertical axis is fixed in space, and wherein thelongitudinal and latitudinal axes move with the entry guide.
 5. Themedical robotic system according to claim 4, wherein the controller isconfigured to command the mechanical elements of the entry guidemanipulator to be moved so as to effect the desired state of the entryguide by: determining a desired velocity of the desired state of theentry guide; and transforming the desired velocity into a linearvelocity along the longitudinal axis, a first rotary velocity about thelongitudinal axis, a second rotary velocity about the latitudinal axis,and a third rotary velocity about the vertical axis.
 6. The medicalrobotic system according to claim 5, wherein the controller isconfigured to compute for each of the plurality of articulatableinstruments, a vector extending from the distal end of the entry guideto a tip of an articulatable instrument of the plurality ofarticulatable instruments, a radial component of the vector being alongthe longitudinal axis, and a tangential component of the vector beingperpendicular to the longitudinal and latitudinal axes.
 7. The medicalrobotic system according to claim 6, wherein the controller isconfigured to apply weighting factors to the radial and tangentialcomponents of the vectors extending from the distal end of the entryguide to the tips of the plurality of articulatable instruments.
 8. Themedical robotic system according to claim 7, wherein the plurality ofarticulatable instruments comprises a plurality of articulatablesurgical tools, and wherein the controller is configured to selectweighting factors so that any individual one of the plurality ofarticulatable surgical tools having a tip that falls outside of a fieldof view of the articulatable camera has a larger weighting factor thanany individual one of the plurality of articulatable surgical toolshaving a tip that does not fall outside of the field of view of thearticulatable camera.
 9. The medical robotic system according to claim8, wherein the respective weighting factors for the plurality ofarticulatable instruments increase in an inversely proportionalrelationship to their respective distances to an anatomic structure thatis to be avoided.
 10. The medical robotic system according to claim 8,wherein the controller is configured to: compute resultant velocityvectors for the tips of the plurality of articulatable instruments, eachof the resultant velocity vectors including first and second parts, thefirst part including contributions from the first, second, and thirdrotary velocities as applied to a Jacobian of the entry guidemanipulator that has been modified for that articulatable instrument,the second part including an additional contribution from the firstrotary velocity; compute a norm for each resultant velocity vector ofthe resultant velocity vectors by dividing a maximum allowable linearvelocity of a tip of the one of the plurality of articulatableinstruments corresponding to the resultant velocity vector by amagnitude of that resultant velocity vector; determine a minimum normamong the computed norms; and apply the minimum norm to scale the first,second, and third rotary velocities if the minimum norm is less thanunity.
 11. The medical robotic system according to claim 10, whereincontroller is configured to modify the Jacobian of the entry guidemanipulator for each of the plurality of articulatable instruments byreplacing a distance of the distal end of the entry guide from theremote center with a radial component projected on the longitudinal axisof the entry guide of a distance of the tip of that articulatableinstrument from the remote center.
 12. The medical robotic systemaccording to claim 11, wherein the second part for each of the resultantvelocity vectors comprises a cross product of a tangential component ofthe tip of the articulatable instrument corresponding to the resultantvelocity vector and the first rotary velocity in the direction of thelongitudinal axis.
 13. The medical robotic system according to claim 1,wherein the controller is configured to cause the plurality of thearticulatable instruments to be controllably held in position relativeto the entry guide as the entry guide is moved.